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92 K75S Fuel injectors are wide open...

Hello everyone,

I hope someone has seen this problem before and can help.

The bike was not running. Fuel coming from the exhaust. I pulled the fuel rail and the injectors are flowing wide open continuously when the start button is pressed and until the fuel pressure stops. I've seen these injectors working before so I do know that these are running continuously not just looking like they are. Massive fuel coming out of all injectors.

Injectors were sent in and cleaned and tested. Injectors are good. Computer, Air Flow sensor, Temp sensor and fuel pressure regulator replaced. Problem still persists.

I disconnected one plug from one fuel injector and that one is not squirting. So the injectors are getting a solid power signal... Kill switch shuts them off instantly. Also disconnected the TPS with no effect.

Could it be a short in the fuel injectors wiring harness .? Or the fuel filter is causing a back pressure?

The last time I saw this, it was caused by a bad FICU. See if you can borrow one from a running bike. It's also possible that your injector switching wire has somehow become grounded. This could be caused by over-zealous use of zip-ties around a harness.

The injectors are powered ON whenever the ignition is on. They are triggered by grounding the other side of the connector. That is grounded by the L-Jetronic unit. They are wired in parallel - ie - they all fire at the same time.

Something is grounding out. Quick check - unplug the L-Jetronic, see if they close. If so - L-Jetronic has problems (almost NEVER happens).

If they then don't close with the ignition on, start following the brown wiring from the injectors backwards toward the harness until you find the ground problem. It's possible the problem is in a harness - which is a real problem to track down but not unknown due to the wire density on K bike harnesses and the small passages the harness is snaked through.

If both are correct - then something is telling the L-Jetronic to fire the injectors.. so it means tracing the wiring to and from the ignition module (located under the seat about dead center in the frame right behind the steering head) since that provides the trigger signal to the L-Jetronic to fire the injectors.

I don't have a wiring diagram handy anymore, but I'm sure someone can help you out. One WAG (and it is a WAG..) might be the hall-effect-sensor wiring may have shorted out, telling the ignition module that it's time to fire the plugs (and inject some fuel.) But that's just a guess.. so don't spend any money trying it until someone tells you what connectors on what device you want to check for an errant signal.

I think I now have a blown head gasket because # 3 plug is coming out black and oily and the bike won't idle or rev over 6K.

Michael

Possible, but highly unlikely. Have you replaced the plugs with NEW ones since the computer issue? If not, it is likely that the plugs are very fuel fouled. You might try cleaning and regaping them (to the tight side). Then put them in different cylinders to see if the problem returns to the same cylinder.

Did all that

When I got the bike from another mechanic the oil view window was already too full so as soon as I got it running (somewhat) I drained it and replaced the oil and filter. I also replaced the plugs with another set.

Compression test shows all cylinders are the same....

I even bought a leak down tester but this is my first time using it and I'm not sure what the results mean.

If using the leakdown tester resulted in air coming out another spark plug hole or into the coolant, you could conclude that the head gasket was blown. I have seen Ks blow gaskets, but it is usualy due to overheating. You have to think about where all that fuel went: into the crankcase, which vents into the plenum chamber. #3 is closest to the vent, so much of that vaporised fuel goes into that cylinder. Replace that plug; they never seem to recover from fouling. Did you change the oil after you installed the working FICU or before?

If the compression test comes out fine, it is unlikely that the head gasket is blown. Did you test for oil in the coolant or coolant in the oil? A blown head gasket will create lots of white smoke and you can test for combustion gas in the coolant.

I am not a K expert but did you check the coil for Cyl #3 by swapping with another cylinder? It sounds like maybe the plug is just not firing. You could also ground the plug and check for spark.